1. Wiepkema, P.R. (1983). On the significance of ethological criteria for the assessment of animal welfare. In D. Smidt (Ed.), Indicators relevant to farm animal welfare, (pp. 71–79). Boston: Martinus Nijhoff.
2. Gray, J.A. (1982). The neuropsychology of anxiety: an enquiry into the functions of the septo-hippocampal system. Oxford: Clarendon.
3. Henry, J.P., & Stephens, P.M. (1977). Stress, health, and the social environment. New York: Springer.
4. Laborit, H. (1986). L’inhibition de l’action. Biologie comportementale et physio-pathologie. Paris: Masson.
5. Warburton, D.M. (1987). The neuropsychobiology of stress response control. In P.R. Wiepkema, & P.M.W, van Adrichem (Eds.), Biology of stress in farm animals: an integrative approach, (pp. 87–100). Dordrecht: Martinus Nijhoff.